Photographic silver halide emulsion with improved safe-light sensitivity

ABSTRACT

LIGHT-SENSITIVE SILVER HALIDE EMULSIONS CONTAINING MIXTURES OF A DIPHENYLDISULFIDE CARBOXYLIC ACID, A POLYHYDROXYSPIRO-BIS-INDANE, A DEVELOPING AGENT AND A POLY(ALKYLENE OXIDE) COMPOUND. THE EMULSIONS HAVE IMPROVED LIGHT-SENSITIVITY WITH REDUCED SENSITIVITY TO SAFE-LIGHT ILLUMINATION.

United States Patent US. Cl. 96-107 8 Claims ABSTRACT OF THE DISCLOSURE Light-sensitive silver halide emulsions containing mixtures of a diphenyldisulfide carboxylic acid, a polyhydroxyspiro-bis-indane, a developing agent and a poly- (alkylene oxide) compound. The emulsions have improved light-sensitivity with reduced sensitivity to safe-light illumination.

BACKGROUND OF THE INVENTION This invention relates to photographic silver halide emulsions that contain combinations of sensitizers having a selective action that increase sensitivity.

It is known that the sensitvity of photographic silver halide emulsions can be increased through the addition of chemical sensitizers. Besides gold and sulfur compounds, poly(ethylene glycols), especialy those with a molecular weight above 1500, have proven to be very useful agents for increasing the sensitivity. In addition, it is also known that chemical sensitizers in combination with suitable stabilizers and, if desired, still other compounds can also be used. With such combinations, considerable increases in the sensitivity are reported without increasing the fog to an objectionable degree. Such combinations are described, for example, in the German patent specifications 1,155,327 and 1,163,672.

In practical use, it has been found that the sensitivityincreasing action of such combinations is not selective only in the blue region of the spectrum, but that marked sensitivity of the emulsion also occurs in the red and, above all, in the green region of the spectrum. This secondary action is more pronounced when more efiective sensitivity-increasing combinations are used. This additional increase in sensitivity in the longer-wave region is very detrimental and undesirable. Silver halide emulsions for radiographic purposes are used in combination with intensifying screens and are sensitive mainly to the blue light of the intensifying screen and in practice are usually processed with red or green safe lights. If now by chemical sensitization not only the sensitivity in the blue region is increased, but the sensitivity in the longer-wave region also is increased, then the photographic emulsion will not possess adequate resistance toward the safe light used in the dark room. This shortcoming is especially pronounced when green safe lights, such as the mercury high-pressure lamps with a line spectrum at 546 III/L and 579 m are used in the dark room. The light radiated by these lamps is agreeably bright to the eye, because its maximum radiation is located in a physiologically favorable region of eye sensitivity. As a result of this extremely favorable property, such lamps facilitate and accelerate the working procedures in the dark room and, therefore, are finding introduction in practice to an increasing extent. A disadvantage is that the highly sensitive silver halide emulsions, especially the bromide-iodide types, are not sutficiently stable toward this comparatively bright light, and fog during the processing.

3,672,902 Patented June 27, 1972 ice This invention provides a highly effective sensitizer combination which markedly increases the sensitivity of the emulsion in the blue region and at the same time desensitizes the longer-wave region, that is, reduces the sensitivity in the red and, above all, in the green region. The goal is to produce highly sensitive emulsions that can be processed with high-intensity, green safe lights without deleterious effects. According to the invention, this problem is solved by adding a diphenyldisulfidedicarboxylic acid, a polyhydroxy-spiro-bis-indane, and a quantity of metol or 3-pyrazolidone insufiicient for complete development, to the light-sensitive silver halide emulsion or to a gelatin-containing layer in contact with it. This combination considerably increases the sensitivity with low fog values and, in fact, selectively in the blue region of the spectrum, whereas, a lowering of the sensitivity is etfected in the longer-wave spectral region, especially in the green region.

From French Pat. 1,395,324, it is known that diphenyldisulfidedicarboxylic acids can be used as stabilizers for photographic materials. The use of polyhydroxy-spiro-bisindanes as tanning developers is known from Belgian Pat. 699,429. Numerous other publications have taught the introduction of developers, such as p-amino-phenols and 3-pyrazolidones, into photographic layers. These materials alone do not yield the effect described above. A combination of the compounds selectively increase the sensitivity in the blue region of the spectrum and lower the sensitivity in the green and red regions. This surprising fact and synergistic effect could not have been predicted from knowledge of the mode of action of the individual components. A considerable and surprising advance is achieved by their synergistic effect.

DESCRIPTION OF THE PREFERRED EMBODIMENT To carry out the process, diphenyldisulfidedicarboxylic acids, especially diphenyldisulfide-2,2'-dicarboxylic acid, already mentioned in French Pat. 1,395,324, can be used. An especially suitable polyhydroxy-spiro-bis-indane compound is 3,3,3',3'-tetramethyl-4,5,4',5-tetrahydroxy-spirobisindane. However, the other compounds mentioned in the Belgian Pat. 699,429 also can be used. A procedure for preparing compounds of this type, according to information in the Belgian patent, is described in J. Chem. Soc. 1934, pages 1678-1681. 3-pyrazolidone developers are known in large numbers, for example, from the British patents 679,677, 679,678, and 767,704. The best-known compound of this group is 1-phenyl-3-pyrazolidone, which is obtainable in the market under the name Phenidone. The compounds of the invention can be added directly to the light-sensitive silver halide emulsion and/or they can be introduced into a gelatin-containing intermediate layer located directly in contact with the emulsion. Accordingly, a part of the combination can be located in the lightsensitive layer and another in the light-insensitive secondary layer.

The compounds are added to the photographic films according to known procedures in a quantity usable for the purpose mentioned. The optimum quantities to be used in a particular case can be determined easily by those skilled in the art and generally amount to about 0.015- 0.120 g. of the diphenyldisulfidedicarboxylic acid, 0.5- 1.50 g. of a polyhydroxy-spiro-bis-indane compound, 0.01-0.10 g. of p-aminophenol, and 0.051.0 g. of 2- phenylpyrazolidone developer per mole of silver halide present in the emulsion. Preferably, the addition takes place after the chemical ripening and before coating the emulsions. The sensitizer combination of the invention is suitable for optically unsensitized silver halide emulsions, preferably for bromide-iodide emulsions such as those used for radiography with and without intensifying screens. The emulsions may contain the customary macromolecular, water-permeable, organic colloid binders, emulsion additives such as hardeners, wetting agents, development accelerators, antifoggants, etc. Especially favorable sensitometric processing results can be achieved if, according to the invention, poly(alkylene oxide) compounds with a molecular weight of preferably 1500- 4000 and more are added to the emulsion as part of the sensitizing system. Suitable poly(alkylene glycols) as well as their condensation products with acids, alcohols or amides and macromolecular water-permeable organic colloid binders are described in US. Pats. 2,240,472, 2,400,532, 2,423,549, 2,441,389, 2,955,037 and 2,965,487. As is known, the action of these poly(alkylene oxide) compounds increase the developing speed or, for the same given developing times, increase the sensitivity of the emulsion. Surprisingly, combinations of poly(alkylene oxide) compounds and the materials described herein produce high sensitivity values in substantially shorter time without the appearance of fog characteristic of these longchain compounds.

The invention is illustrated, but not restricted, by the following examples:

EXAMPLE 1 An optically unsensitized, highly sensitive silver halide emulsion is produced containing about gelatin and about silver halide. The silver halide consists of 98 weight percent AgBr and 2 weight percent of silver iodide. Added to this emulsion per mole of silver halide are 0.03 g. diphenyldisulfide-2,2-dicarboxylic acid 0.05 g. metol 1.0 g. 3,3,3',3' tetramethyl-5,6,5, -tetrahydroxy-spirobis-indane G. Hydroquinone 30 1-phenyl-3-pyrazolidone 1 Na SO (anhydrous) 60 KOH 23 NaBO,-4H 0 20 Water to 1 liter.

The film was fixed in a customary fixing bath, subsequently washed and dried. The following results were obtained in which, for simple comparison, the values for the general sensitivity and the green sensitivity of the comparison emulsion were set equal to 100. In addition, the ratio of general sensitivity/green sensitivity (K) is given.

General] Relative green General green so sensisensitivit Sample tivity tivlty (Kg Fog Comparison emulsion 100 100 1. 00 0. 07 Emulsion of the invention. 165 63 2. 63 0. 06

The following method was used to test the safe-light sensitivity of the film:

The test strips were exposed to a mercury high-pressure lamp with a line spectrum at 546 and 579 m, at a distance of 70 cm. continuously increasing from 0 to 10 min. The samples were then developed in a metol-hydroquinone developer and the exposure time required to produce a density of 0.1 above fog determined.

EXAMPLE 2 The following constituents were added, per mole of silver bromide, to an emulsion produced according to Example 1:

0.03 g. diphenyldisulfide-2,2'-dicarboxylic acid 0.90 g. l-phenyl-3-pyrazolidone 1.0 g. 3,3,3, '-tetramethyl-5,6,5,6'-tetrahydroxyspiro-bis-indane The samples were then processed and evaluated analogous to the data in Example 1. The results obtained are compiled in the table:

General] Relative green General green sensisensisensitivity Sample tivity tivlty (K) Fog Comparison emulsion 100 1. 00 0. 07 Emulsion of the invention 155 64 2. 43 0. 0!.

EXAMPLE 3 The following constituents were added, per mole of silver bromide, to an emulsion produced according to the data in Example 1:

tion given in Example 1 for 60 sec. at 27 C. The results following results were obtained thereby:

General/ Relative green General green sensise sensiflviy Sample tivity tivity Fog Comparison emulsion 100 100 l. 00 0. 07 Emulsion of the invention. 59 2. 46 0. 05

EXAMPLE 4 The following constituents were added, per mole of silver bromide, to an emulsion produced according to thedata in Example 1:

0.03 g. diphenyl-2,2'-dicarboxylic acid 0.20 g. l-phenyl-S-pyrazolidone 1.00 g. 3,3,3',3'-tetramethyl-5,6,5',6'-tetrahydroxyspiro-bis-indane 1.00 g. carbowax 4000 The samples were then treated with the developer solution given in Example 1 for 6 sec. at 27 C. The results obtained are compiled in the table:

General] Relative green General green sensisens1- sensitivity Sample tivity tivity (K) Fog Comparison emulsion 100 100 1. 00 0. 07 Emulsion of the invention. 63 2. 40 0. 04

From Examples 3 and 4, it is evident that in the presence of poly(ethylene oxide) compounds, the increase in sensitivity can be reached even with shorter processing times.

EXAMPLE 5 To demonstrate the mode of action of the described combination, the compounds of the invention were added, individually and in combination with one another, to the light-sensitive emulsion described in Example 1. The in- 2. Silver halide emulsion according to claim 1, chardividual compounds are indicated as follows: acterized in that it contains diphenyldisulfide-2,2'-dicarboxylic acid.

gfgyf gg ig gs ggi figfifi fig ggfi 4000) 3. Silver halide emulsion according to claim 1, chari y 5 acterized in that it contains 3,3,3,3'-tetramethyl-5,6,5',6-

Hib1-phenyl-3-pyrazolidone z g lg 'fi l 1 h iver ar e em sion accor mg to calm c arj g tetramethyl tetrahydroxy Spiro acterized in that it contains N-methyl-p-aminophenol.

5. Silver halide emulsion according to claim 1, char- The results obtained on processing with the developer 10 agterized in that it contains 1-pheny1-3-pyrazolidone,

solution given in Example 1 with a developing time of 6. Silver halide emulsion according to claim 1, charsec. at 27 C. are compiledinthe table: aeterized in that, in addition, it contains a polyethylene Grams 0t substance introduced per mole AgBr Relative General! General green green I II IIa. Illb IV sensitivity sensitivity sensitivity Fog O 0 0 0 0 100 1. 00 0. 07 1 0 0 0 0 143 0. 84 0. l1 0 0 0 0 1 106 67 l. 58 0. 05 l 0 0 0 1 72 l. 80 0. 05 0 O. 03 0 0 1 100 67 1. 50 0. 05 0 0 0 0. 9 l 127 51 2. 50 0. 06 0 0 0. 05 0 l 115 53 2. 20 0. 05 1 0. 03 0 0 0 91 1. 60 0. 08 0 0. 03 0. 05 0 0 77 2. 15 0. 07 0 0. 03 0 0. 8 0 145 82 1. 77 0. 08 1 0. 03 0 0. 9 0 145 82 1. 77 0. 10 1 0. 03 0. 05 0 0 77 2. 28 0. 11 1 0 0. 05 0 1 135 59 2. 29 0. 06 1 0. 03 0 0 1 141 65 2. l7 0. 05 0 0. 03 0. 05 0 l 165 63 2. 62 0. 05 0 0. 03 0 0. 3 1 145 59 2. 46 0. 05 0 0. 03 0 0. 9 1 155 63 2. 46 0. 04 1 0. 03 0. O5 0 1 61 3. 05 0. 07 1 0. 03 0 0. 9 1 56 3. 48 0. 07

The great advantage of this invention is that it offers glycol compound with a molecular weight of at least the possibility of producing emulsions for radiography 35 1500. with intensifying screens, the sensitivity of which can be 7. A silver halide emulsion according to claim 1, whereincreased selectively in the blue region of the spectrum, in the constituents are present in the amounts 0.015- while at the same time reducing the sensitivity in the long- 0.120, 0.5-1.50, 0.01-0.10, and 0.051.0 gram, respectivewave region, especially in the adjacent green region, so 1y, per mole of silver halide. that these emulsions can be processed in high-intensity 4 8. An emulsion according to claim 7 which is a gelatinogreen safe lights without deleterious side effects. An addisilver bromide-iodide emulsion.

tional advantage is that the combination described is characterized as being very stable so that emulsions with an References Cited improved sensitivity/fog ratio can be obtained. In the UNITED STATES PATENTS presence of poly(alkylene oxide) compounds, this im- 45 proved sensitivity/fog ratio is achieved at substantially 3403025 9/1968 et 96 107 shorter developing times 3,518,085 6/1970 Milton et al. 96-107 The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: NORMAN TORCHIN Pnmary Exammer 1. Optically unsensitized, highly sensitive photographic 50 R. E. FICHTER, Assistant Examiner silver halide emulsion, characterized in that it contains a diphenyldisulfidedicarboxylie acid, a polyhydroxy-spiro- US. Cl. X.R. bis-indane and a p-aminophenol or a 3-pyrazolidone de- 96-101 veloping agent. 

